Field of the Invention
The present invention relates to a raw setter, and a firing method of a honeycomb formed body. More particularly, it relates to a raw setter which is used for firing an unfired honeycomb formed body extruded by using an extruder, in a firing furnace, and a firing method of a honeycomb formed body.
Description of the Related Art
Heretofore, a honeycomb structure made of ceramics has broadly been used in a use application such as a car exhaust gas purifying catalyst carrier, a diesel particulate removing filter, or a heat accumulating body for a burning device. The honeycomb structure made of the ceramics (hereinafter simply referred to as “the honeycomb structure”) is manufactured by preparing a forming material (a kneaded material), extruding the material into a desirable honeycomb shape by use of an extruder, followed by raw cutting, drying and finish-cutting, and then subjecting the material through a firing step of firing the material at a high temperature.
In the above firing step, the honeycomb formed body is loaded on a shelf plate in a state where one end face of the honeycomb formed body is directed downward, and the honeycomb formed body and the shelf plate are then loaded into a firing furnace. At this time, to prevent the honeycomb formed body from being adhered to the shelf plate, a firing support plate referred to as “a setter” is interposed between the support plate and the honeycomb formed body. As to this setter, a cut piece of the honeycomb structure firing the honeycomb formed body has been used as the honeycomb formed body firing setter, but when the setter is repeatedly used, cracks are generated. Therefore, a press-molded and fired ceramic raw material referred to as “a pressed setter” is used, and hence, the material can be used repeatedly (e.g., see Patent Document 1). Such a setter is generically referred to as “a firing setter”. In the present description, the extruded body prior to the firing is called “the honeycomb formed body”, and the fired body is referred to as the honeycomb structure.
The extruded honeycomb formed body carries out a firing shrinkage along a longitudinal direction of cells and a direction orthogonal to the cell longitudinal direction in the firing step. Therefore, when the honeycomb formed body is mounted on the above firing setter and loaded into the firing furnace, a shift occurs between an upper surface of the firing setter and a lower end face of the honeycomb formed body due to the firing shrinkage of the honeycomb formed body, and defects such as deformation and fissures of cell partition walls might be generated in the lower end face of the honeycomb structure which comes in contact with the firing setter. In addition, the lower end face of the honeycomb formed body is stuck on the upper surface of the firing setter, the shift does not evenly occur, and a shape of the lower end face of the honeycomb structure might be curved. When the curving occurs, a round pillar-shaped honeycomb structure has a roundness defect in its end face. In particular, when the honeycomb formed body is fired in which cell partition walls defining a plurality of cells have a small thickness, the above defects are remarkably generated.
Thus, when the honeycomb formed body is fired in which the cell partition walls are thin, a raw setter which is cutting an unfired honeycomb formed body made of the same material as the honeycomb formed body (hereinafter simply referred to as “the raw setter”) is used in the firing step. A firing shrinkage difference is not made between the raw setter and the honeycomb formed body of a firing object during the firing, and the raw setter can carry out the firing shrinkage at the same timing and the same ratio as the honeycomb formed body along the cell longitudinal direction and a cross sectional direction orthogonal to the cell longitudinal direction. Consequently, in the firing step, any resistances or restraints are not generated between the honeycomb formed body and the raw setter, and the problem of a shape defect such as a defect of each end face cell partition wall or the roundness defect can be eliminated. Furthermore, it is known that a shape or a surface roughness of the upper surface of the raw setter which comes in contact with the lower end face of the honeycomb formed body is regulated, and hence, an influence on the lower end face of the honeycomb formed body can be alleviated even when a slight shift occurs (e.g., see Patent Document 2).
[Patent Document 1] JP-A-2000-274954
[Patent Document 2] WO2006/035674A1